function(test)


  map_fill("{a:null,b:1,c:2}" "{a:3,d:4}")
  ans(res)
  assertf("{res.a}" STREQUAL "3")
  assertf("{res.b}" STREQUAL "1")
  assertf("{res.c}" STREQUAL "2")
  assertf("{res.d}" STREQUAL "4")


endfunction()